چکیده انگلیسی

Attention-Deficit Hyperactivity Disorder (ADHD) is no longer believed to be a time-limited syndrome manifested in and restricted to childhood and adolescence. Many of the characteristics associated with the disorder continue in variable form into adulthood. This investigation focused on two measures sensitive to attention, cognitive flexibility, and visual and auditory distraction, to determine if individuals diagnosed with ADHD would perform poorly in comparison with normal control subjects. Forty-two subjects, 27 ADHD adults and 15 control subjects, were administered the Goldman-Fristoe-Woodcock Test of Auditory Discrimination (TOAD), and the Stroop Color and Word Test. The findings indicated that the TOAD Noise subtest significantly discriminated the subjects, resulting in an overall correct classification rate of 80.95%.

مقدمه انگلیسی

A pervasive developmental disorder characterized by inattention, restlessness, and impulsivity was first identified by Still (1902). This behavioral constellation has had many diagnostic labels, including, hyperkinesis, hyperactive child syndrome, and minimal brain damage. According to the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; American Psychiatric Association, 1994), the essential features of inattention, behavioral disinhibition, and hyperactivity are classified as attention-deficit hyperactivity disorder (ADHD), which affects an estimated 3 to 5% of all children.
ADHD appears to be the most common psychological diagnosis among children in this country. Clinically, it accounts for up to 12 to 36% of the caseload in outpatient clinics depending on diagnostic methodology (Cohen, Riccio, & Gonzales, 1994). Regarding gender, Barkley (1990) reports that ADHD occurs in males roughly three times more often than in girls. However, McGee, Williams, and Silva (1987) suggest that ADHD occurs as frequently in females as in males. They purport that girls may be diagnosed less often because their symptoms are not as blatantly active or aggressive as male subjects.
It is believed that brain function is impaired to some degree in the child evidencing ADHD. Lou, Henriksen, and Bruhn (1984) established that these children have hypoperfusion in the central white matter of the frontal lobes and in the caudate nucleus relative to the normal perfusion observed in non-ADHD children. Furthermore, the diminished perfusion to the striatum and orbital prefrontal regions is observed more in the right hemisphere than in the left hemishpere (Lou, Henriksen, Bruhn, Borner, & Nielsen, 1989). More recent investigations have documented differences in anatomical mass (Semrud-Clikeman et al., 1994), cerebral volume (Castellanos et al., 1996), glucose metabolism (Zametkin et al., 1990), and hemispheric anomalies (Filipek et al., 1997) in individuals with ADHD. For a comprehensive review of the neurological basis of ADHD, the reader is directed to Riccio, Hynd, Cohen, and Gonzalez (1993).
Consistent with these findings, magnetic resonance imaging (MRI) reveals that the brains of ADHD children do not show the normal frontal asymmetry, with the right being larger than the left (Hynd, Semrud-Clikeman, Lorys, Novey, & Eliopulos, 1990). Instead, ADHD children exhibit a smaller right frontal width, resulting in symmetrical frontal lobes. Other studies examining the neuroanatomy of ADHD have also implicated a right hemisphere dysfunction Branch, Cohen, & Hynd 1995, Brumback & Staton 1982, Heilman, Voeller, & Nadeau 1991, Schaughency & Hynd 1989, Semrud-Clikeman et al. 1996 and Voeller 1986. In addition, the right hemisphere has been implicated in other unique tasks relevant to this investigation, such as color identification (Golden, 1978).
In particular, the frontal lobes and related functions are implicated in the symptomology of ADHD (Zametkin et al., 1990). The frontal lobes are considered the area of the brain that controls the executive functions Luria 1966 and Stuss & Benson 1986. In addition, behavioral disinhibition, inattention, and restlessness are thought to be associated with impairments in the frontal lobes Grodzinsky & Diamond 1992 and Lou et al. 1984. Effects of lesions to the frontal lobe often result in a disinhibition syndrome consisting of inappropriate affective responses coupled with the disinhibition of impulses Luria 1973, Damasio & Van Hoesen 1983 and Tucker 1986.
Biederman, Newcorn, and Sprich (1991) reported on the extremely high levels of comorbidity of ADHD among clinical and epidemiological samples. Siedman et al. (1995) hypothesized that comorbidity, familial history, and learning disabilities might affect the pattern and severity of the ADHD symptoms and neuropsychological performance. They found that ADHD children performed at comparable levels on neuropsychological tests with and without the presence of psychiatric comorbidity. Two factors, family history and learning disabilities, were correlated with poorer test performance and outcome in ADHD children. The presence or absence of learning disabilities further complicates the heterogeneous nature of the ADHD population. Barkley (1990) reports a conservative estimate of between 19% and 26% of ADHD children are codiagnosed with at least one type of learning disability. Although the co-occurrence of learning disabilities is not established in the adult population, it is expected that the frequency is comparable to that observed in children (Nadeau, 1995). Several researchers have investigated the comorbidity of ADHD in children with disabilities in reading Gillis, Gilger, Pennington, & DeFries 1992 and Pennington, Groisser, & Welsh 1993, visual-spatial abilities (Swanson et al., 1991), language (Cantwell & Baker, 1987), and mathematics (Ackerman, Anhalt, & Dykman, 1986).
In the current diagnostic definition of ADHD, deficits in attentional ability is one of the defining characteristics. Recent investigations have focused on particular aspects of attention, in part to disentangle the influence of behavioral and cognitive factors to ADHD and comorbid conditions. Specifically, auditory attentional abilities have been investigated in children with ADHD via continuous performance testing Riccio et al. 1994 and Riccio et al. 1996 and dichotic listening tasks Pearson et al. 1991 and Prior et al. 1985. Results from these studies indicate that ADHD children appear to exhibit reduced ability to process auditory information when required to divide and focus their attention for a sustained period of time (Riccio et al. 1996 and Pearson et al. 1991; Prior et al., 1984). However, Keith and Engineer (1991) have hypothesized that the observed auditory and linguistic problems are primarily attributed to an underlying learning disability as opposed to ADHD.
Previously, it was suggested that ADHD was a time-limited syndrome manifested in and restricted to childhood and adolescence. However, it is now widely accepted that many of the attentional difficulties and related clinical features may persist in variable form into adulthood Biederman et al. 1993, Caresia et al. 1984 and Denckla 1991. Prospective long-term follow-up studies with blind assessment of probands and controls have demonstrated the persistence into adulthood in roughly 30 to 50% of individuals previously diagnosed in childhood Gittelman, Manuzza, Shenker, & Bonagura 1985, Mannuzza, Klein, Bonagura, Konig, & Shenker 1988, Mannuzza et al. 1991 and Weiss, Hechtman, Milroy, & Perlman 1985. ADHD in adults is often manifested in vocational difficulties, frequent job changes, and instability in important intimate relationships Nadeau 1995 and Weiss & Hechtman 1993. Many of the studies examining adult ADHD are retrospective in nature and are confounded by the presence of other psychiatric disorders, namely alcoholism (Tarter, McBride, Buonpane, & Schneider, 1977), psychoses (Bellak, 1977), conduct disorder, and antisocial personality disorder Kaminer 1992 and Milman 1979.
The clinician is challenged by issues pertaining to both comorbidity and differential diagnosis. Individuals with ADHD are at risk for developing a variety of symptoms related to antisocial behavior, affective disorders, intermittent explosive disorder, and substance abuse Biederman, Munir, & Knee 1987, Gomez, Janowsky, Zetin, Huey, & Clopton 1981, Morrison & Minkoff 1975 and Tarter et al. 1977. Conversely, many of the patients with these disorders endorse many of the hallmark symptoms of ADHD (Barkley, 1990). Notably, higher rates of depression and low self-esteem have been observed in children and adults with ADHD Biederman et al. 1993, Faraone & Biederman 1997, Spencer et al. 1995 and Wilens et al. 1995. The symptoms of inattention, irritability, and low frustration tolerance may be evident in both depression and ADHD (Tzelepis, Schubiner, & Warbasse, 1995). Interestingly, it has frequently been suggested that depressed individuals demonstrate a pattern of suppressed right hemisphere functions, especially on spatial and timed tasks Cassens et al. 1990 and Flor-Henry 1976.
Presently, standardized assessment instruments, comparable to those available for children and adolescents, pertaining to the achievement ability of adults are lacking. The adult diagnosis is further complicated by dependence on retrospective, self-report data. Moreover, there is evidence that some of the characteristics (e.g., hyperactivity) and treatment response in adults with ADHD may be manifested differently from those in children Spencer et al. 1995 and Wender 1997. Weiss and Hechtman (1993) report that more than half of the adults in their investigations who were diagnosed hyperactive as children reported the continuance of at least one disabling symptom of the syndrome. However, the implication is that many of the adults seem to outgrow or learn to manage the symptoms. The picture becomes even more complicated for the majority of the recently identified ADHD adults who were never diagnosed in childhood (Wender, 1997).
The most common treatment for ADHD is stimulant medication Saccar 1978 and Schachar & Tannock 1993. Stimulant use has been investigated extensively in children, but to a much lesser degree in adults (Bhandary, Fernandez, Gregory, Tucker, & Masand, 1997). These medications increase the utility of aminergic neurotransmitters, namely norepinephrine and dopamine. In addition, the administration of stimulant medication improves perfusion in ADHD individuals (Lou et al., 1984).
It is estimated that 75% of children diagnosed with ADHD are primarily treated with psychostimulants (Schachar & Tannock, 1993). Studies assessing the efficacy of medications help to elucidate the mechanism of action of the stimulant drug and possibly the pathophysiology of ADHD (Zametkin & Rapoport, 1986). It appears that adults evidencing ADHD may respond differently to stimulant medications, implying distinctly different clinical characteristics (Mattes, Boswell, & Oliver, 1984). Caresia et al. (1984) distinguished response to Pemoline treatment in ADHD children and adults. The adult responders to the medication exhibited a different physiological effect (electroencephalogram [EEG] pattern) and reported subjective paradoxical calming after administration of the drug. The children, on the other hand, did not demonstrate similar EEG changes or behavioral responses. Apparently, despite the increasing use of such medications for adults, roughly 30 to 50% are nonresponders, experience unfavorable side effects, or have concommitant depressive or anxiety disorders Biederman et al. 1993 and Spencer et al. 1995. Such findings imply modified diagnostic, therapeutic, and prognostic criteria for adults evidencing ADHD.
Furthermore, adults whose symptoms have persisted into adulthood may have masked signs and be attempting to compensate for their difficulties via self-medication with cocaine Cocores et al. 1987 and Weiss & Mirin 1986, caffeine (Dalby, 1985), alcohol (Tarter et al., 1977), nicotine and other drugs Conners et al. 1996 and Hartsough & Lambert 1987. Also, Rugle and Melamed (1993) reported that a disproportionate number of pathological gamblers demonstrated deficits in executive, frontally mediated, attention processes, and concomitantly exaggerated childhood behaviors that are consistent with attention deficits. Therefore, the accurate assessment of the disorder in adults is imperative for explanatory and treatment purposes. The affect of ADHD symptomology can be pervasive, essentially impacting every functional area of the affected adult’s life (i.e., social, occupational, legal). Conversely, the overall benefits of “… successful treatment may very well prove to be of life-changing proportions” (Wender, 1997, p. 561).
Traditionally, there has been no accepted screening battery developed for the assessment of ADHD in adults, or children for that matter. Currently, it appears that the most sensitive and useful diagnostic tool is a well-constructed clinical interview (Brown, 1995). However, guidelines have been proposed for the assessment of children (Barkley, 1990) and adults (Wender, 1995). The Luria-Nebraska Neuropsychological Battery-Children’s Revision failed to discriminate ADHD from controls (Schaughency et al., 1989). In the past decade, several neuropsychological instruments have been studied for diagnosing children and adolescents with ADHD. Barkley, Grodzinsky, and DuPaul (1992) reviewed 22 neuropsychological studies of frontal lobe functions in children with ADHD, with and without hyperactivity. Results across studies using similar or comparable instrumentation were inconsistent, and the findings appeared to be strongly related to the age of the subjects.
However, one measure that has been used to assess functioning in ADHD children is the Stroop Color and Word Test (Golden, 1978). This test has been utilized in the measurement of cognitive interference in children (Lufi, Cohen, Parish-Plass, 1990), selective attention in preadolescents (Lavoie & Charlebois, 1994), and prefrontal dysfunction in adults (Trichard et al., 1995). The Stroop was able to discriminate ADHD from normal children (Grodzinsky, 1990) and differentiated ADHD children from those with attention-deficit disorder without hyperactivity (ADD-H; Barkley et al., 1992). However, the Stroop demonstrated only modest positive predictive power (sensitivity, .64) and negative predictive values (specificity, .55) in another study analyzing the accuracy of classification in children with ADHD and ADD-H (Barkley & Grodzinsky, 1994).
The Stroop test is based on the idea that color naming, a more complicated task, takes longer to complete than the simple reading of words. The Stroop has been shown to be sensitive to impairment with concentration, attention, and response inhibition in adults (Lezak, 1995). Therefore, it may be useful in the assessment of adults suspected of having ADHD (Kane, Mikalac, Benjamin, & Barkley, 1990).
Another instrument that appears promising in identifying deficits in auditory attention and information processing is the Goldman-Fristoe-Woodcock Test of Auditory Discrimination (TOAD; Goldman, Fristoe, & Woodcock, 1970). The TOAD has generally been used in the assessment of speech-sound discrimination deficits Bountress 1984 and Klein et al. 1995. However, the TOAD has demonstrated sensitivity in identifying children with auditory language processing problems and high levels of distractibility (Sanger, Keith, & Maher, 1987) and is recommended as a sensitive measure of distractibility in adults with attentional impairment (Sohlberg & Mateer, 1989). This measure provides auditory discrimination under ideal listening conditions, as well as in the presence of noise distraction. It is this latter condition of background noise that is analogous to everyday conditions and provides a sensitive measure of distraction and behavioral disinhibition. Moreover, the TOAD has norms applicable to an adult population.
Pilot data revealed that ADHD adults differed significantly from normal controls in terms of their performance on the aforementioned measures (Corbett & Stanczak, 1996). Other measures of cognitive functioning, such as the Shipley Institute of Living Scale (Shipley, 1946), and academic performance, such as the Peabody Individual Achievement Test-Revised (Markwardt, 1989) were not administered in the present investigation because they consistently failed to discriminate ADHD from control subjects. In addition, other instruments that have been recommended for the assessment of adults with ADHD, such as the Paced Auditory Serial Addition Test (PASAT; Gronwall, 1977) and the Trail Making Test (Reitan & Wolfson, 1993), have consistently failed to discriminate ADHD adults from control subjects in our lab. Thus, the TOAD and Stroop Color and Word Test were chosen for further study. It was hypothesized that these tests would differentiate ADHD adults from normal controls at statistically and clinically significant rates.